A vehicle air bag module is a complete air bag unit which is assembled apart from the vehicle and then coupled as a unit with the vehicle. Typically, an air bag module includes (i) a reaction device, (ii) a folded air bag connected to the reaction device, (iii) an inflator, or gas generator, connected to the reaction device, and (iv) a cover connected to the reaction device to complete an enclosure for the folded air bag. The module is generally coupled with a structural part of the vehicle via the reaction device. In the case of a passenger side air bag module, for example the reaction device may be coupled with the support structure for the vehicle dashboard, and the cover of the module may form a part of the dashboard. Alternatively, in the case of a driver side air bag module, the reaction device may be coupled with the steering wheel support structure, and the cover of the module may form a part of the steering wheel cover.
When coupled with a vehicle, an air bag module operates to deploy an air bag at the onset of a vehicle collision. Specifically, at the onset of a collision, large quantities of gas under relatively high pressure are discharged from the inflator as a result of the ignition of a gas-generating chemical mixture in the inflator and/or the release of gas stored under pressure in the inflator. The cover is designed so that when such gas is discharged from the inflator, portions of the cover can separate to create a deployment opening for the air bag. The gas simultaneously (i) forces the air bag through the deployment opening in the cover and (ii) inflates the air bag. As the air bag is being deployed and inflated, relatively high forces are applied to the various components of the air bag module. The reaction device transmits such forces to the vehicle structure from the air bag module during deployment of the air bag.
In the air bag industry, new and more cost-effective techniques for forming air bag modules are becoming increasingly important. Air bag modules are currently being installed in a large number of automobiles. The number of air bag modules installed in the future will continue to increase, as consumer demand and federal regulatory requirements for vehicle safety also continue to increase. To enable auto makers to meet this growing demand, there is a continuing need for simple and effective techniques which lend themselves to mass production and preferably automation, of air bag modules.
In many existing air bag modules, the reaction device forms a receptacle with a cavity for storing the air bag prior to deployment. This type of reaction device is commonly called a "reaction can". In applicants' experience, a reaction can is usually formed by bolting, riveting or welding together several components. While such "multi-piece" reaction cans have proven satisfactory, they sometimes are not particularly suited for automated assembly. More specifically, in order to automate the assembly of a multi-piece reaction can, it would be necessary to automate the steps of aligning or positioning the various components in their correct orientations and the steps of bolting, riveting or welding these aligned components to each other.
Additionally, in many known air bag module designs, the manner in which the air bag is attached to the reaction can presents further problems in terms of automating the production of such modules. For example, in the interest of minimizing the overall size of an air bag module, it is well known to rivet the mouth of the air bag to the inside surface of the reaction device. However, this fastening technique requires the use of blind rivets which may complicate automated assembly and which present problems in inspecting the quality of the rivets in an efficient manner. Additionally, such a technique requires the rivets to be driven from a variety of directions, which further complicates automated assembly.
Still another issue which affects automated assembly of air bag modules is the attachment of the inflator to the reaction can. Many air bag modules are designed to include an inflator which is commonly referred to as "cylindrical" (i.e., an inflator having an axial length larger than its diameter). These cylindrical inflators present their own problems in regard to automation of the assembly of air bag modules. For example, it is well known to load a cylindrical inflator axially into a reaction can through a wall of the can. Such axial loading is usually difficult to accomplish by automation, especially with live inflators.
In addition to the inflator attachment being incompatible with automated assembly, the subsequent positioning of the inflator within the reaction can may also conflict with the general industry recognized desire to minimize the overall size of an air bag module. More particularly, in many air bag module designs, the cylindrical inflator is disposed completely within the reaction can, and thus occupies a significant portion of the air bag cavity. Additionally, in many applications, assembly tolerances and techniques result in an "thermal insulation barrier" or an empty space between the inflator and the rear portion of the reaction can. Thus, in some air bag module designs, the reaction can must be large enough to accommodate the entire cylindrical inflator and house at least a portion of the folded air bag.
Many existing air bag module designs make it difficult to incorporate lightweight materials (e.g., aluminum) in both the reaction can and the housing of the inflator. This difficulty is the result of the thermal insulation barrier delaying the transmission of ambient heat to the inflator. The delay may retard the onset of auto ignition of the gas generating chemical mixture in the inflator, thereby making it more difficult for an aluminum reaction can, for example, to withstand the temperatures required to initiate auto ignition during a "bonfire" test.
These and other concerns have affected and continue to affect the design of air bag modules. For example, a more recent approach to the assembly of a cylindrical inflator with an air bag module is disclosed in U.S. Pat. No. 4,915,410 to Bachelder. In Bachelder, a cylindrical inflator is "back loaded" into a module after the air bag has been preassembled into the module. The cylindrical inflator is inserted into and aligned in a cradle formed in a reaction plate. A spring clip is then attached to the reaction plate to maintain the cylindrical inflator in the cradle. In order to automate assembly of such a module, it would appear to be necessary first to align the inflator in the cradle, and then attach the spring clip to the reaction plate.
Two other concepts for facilitating the assembly of air bag modules are disclosed in two co-pending applications assigned to the assignee of the present application, namely Ser. No. 07/539,023 to Paquette et al., filed Jun. 15, 1990 and Ser. No. 07/493,962 to Augustitus et. al., filed Mar. 15, 1990. In each of these two applications, an air bag/cover subassembly and a reaction device/inflator subassembly are separately formed and subsequently are connected to each other to complete the air bag module.
Despite such advances in the design of air bag modules, applicants believe a continuing need exists for air bag module structures and assembly techniques which (i) minimize the components required to construct the modules, (ii) minimize the weight and size of individual module components, (iii) reduce the costs and simplify the techniques for manufacturing such individual components, and (iv) simplify the techniques for assembling the modules.